1. Field
This invention relates to an iron-based amorphous alloy core with a saturation magnetic induction exceeding 1.6 Tesla and adapted for use in magnetic devices which require a low magnetic loss and a low level of audible noises during their operation, including transformers, motors and generators, pulse generators and compressors, magnetic switches, and magnetic inductors for chokes and energy storage.
2. Description of the Related Art
Iron-based amorphous alloys have been utilized in electrical utility transformers, industrial transformers, in pulse generators and compressors based on magnetic switches, electrical chokes and energy-storing power inductors. In electrical utility and industrial transformers, iron-based amorphous alloys exhibit no-load or core loss which is about ¼ that of a conventional silicon-steel widely used for the same applications operated at an AC frequency of 50/60 Hz. Since these transformers are in operation 24 hours a day, the total transformer loss worldwide may be reduced considerably by using such magnetic devices. The reduced loss means less energy generation, which in turn translates into reduced CO2 emission.
For example, according to a recent study conducted by the International Energy Agency in Paris, France, an estimate for energy savings in the Organization for Economic Co-operation and Development (OECD) countries alone that would occur by replacing all existing silicon-steel based units was about 150 terawatt-hours (TWh) in year 2000, which corresponds to about 75 million ton/year of CO2 gas reduction. The transformer core materials based on the existing iron-rich amorphous alloys have saturation inductions Bs less than 1.6 Tesla. The saturation induction Bs is defined as the magnetic induction B at its magnetic saturation when a magnetic material is under excitation with an applied field H. Compared with a Bs of ˜2 Tesla for a conventional grain-oriented silicon-steel, the lower saturation inductions of the amorphous alloys lead to an increased transformer core size. It is thus desired that the saturation induction levels of iron-based amorphous alloys be increased to levels higher than the current levels of 1.56-1.6 Tesla.
In motors and generators, a significant amount of magnetic flux or induction is lost in the air gap between rotors and stators. It is thus desirable to use a magnetic material with a saturation induction or flux density as high as possible. A higher saturation induction or flux density in such devices means a smaller size device, which is desirable.
Magnetic switches utilized in pulse generation and compression require magnetic materials with high saturation inductions, high BH squareness ratios, defined as the ratios of the magnetic induction B at H=0 and Bs, low magnetic loss under AC excitation and small coercivity Hc, which is defined as the field at which the magnetic induction B becomes zero, and low magnetic loss under high pulse rate excitation. Although commercially available iron-based amorphous alloys have been used for such applications, namely in cores of magnetic switches for particle accelerators, Bs values higher than 1.56-1.6 Tesla are desirable to achieve higher particle acceleration voltages, which are directly proportional to Bs values. A lower coercivity Hc and a higher BH squareness ratio mean a lower required input energy for the magnetic switch operation. Furthermore a lower magnetic loss under AC excitation increases the overall efficiency of a pulse generation and compression circuit. Thus, there is clearly needed an iron-based amorphous alloy with a saturation induction higher than Bs=1.6 Tesla, with Hc as small as possible and the squareness ratio B(H=0)/Bs as high as possible, exhibiting low AC magnetic loss in a finished magnetic core. The magnetic requirements for pulse generation and compression and actual comparison among candidate magnetic materials was summarized by A. W. Molvik and A. Faltens in Physical Review Special Topics-Accelerators and Beams, Volume 5, 080401 (2002) published by the American Physical Society.
In a magnetic inductor used as an electrical choke or a power inductor for temporary energy storage, a higher saturation induction of the core material brings about an increased current-carrying capability or a reduced device size for a given current-carrying limit. When such devices are operated under AC excitation, the core material must exhibit low core losses. Thus, a magnetic material with a high saturation induction and a low core loss under AC excitation is desirable in such applications.
In all of the above applications, which are just a few representatives of magnetic applications of a material, a high saturation induction material with a low AC magnetic loss is needed as a core material. It is thus an aspect of the present application to provide such materials based on iron-based amorphous alloys which exhibit saturation magnetic induction levels exceeding 1.6 T, and which are close to an upper limit of commercially available amorphous iron-based alloys.
Attempts were made in the past to achieve an iron-based amorphous alloy with a saturation induction higher than 1.6 T. One such example is a commercially available METGLAS®2605CO alloy with a saturation induction of 1.8 T. This alloy contains 17 at. % Co, and therefore is too expensive to be utilized in commercial magnetic products such as transformers and motors. Other examples include amorphous Fe—B—C alloys as taught in U.S. Pat. No. 4,226,619. Such alloys were found mechanically too brittle to be practically utilized. Amorphous Fe—B—Si—M alloys where M=C, as is taught in U.S. Pat. No. 4,437,907, were intended to achieve high saturation inductions, but were found to exhibit Bs<1.6 T.
Generally transformer loss can be reduced by increasing its physical size, which in turn increases its manufacturing cost. It would then be desirable to invent a transformer core with low magnetic loss without increasing its size. Reduction of transformer size is only possible when a transformer is operated at a higher operating magnetic flux density, which generally increases transformer loss and noise.
Thus, there is a need for smaller-sized transformers that achieve lower core loss and lower audible noise simultaneously.